Metallic ingots, notably aluminum, copper, steel and the like, are routinely produced from molten metal using the direct chill (DC) method. In this method of ingot production, a table is positioned beneath a plate having one or more molds mounted therethrough, which plate is fed molten metal, with water being aimed at the sides of the mold. This water chills the molten metal and causes solidification of the metal. The table is lowered and additional molten metal is continuously added to the top of the ingot, chilled and solidified, eventually resulting in a complete ingot which may have a length of 200 inches (508 centimeters) or more.
Control of the vertical movement of the table beneath the mold or molds is vital to successful ingot production. If the table is lowered too slowly, an excessive cooling rate for the metal occurs, resulting in cracks in the ingot and a useless product. On the other hand, should the table be lowered too quickly, insufficient solidification of the metal may occur, resulting in spilling into the casting pit of molten metal.
Thus, for each metal composition, there is an ideal rate of mold velocity, based upon the metal temperature, the size of the mold, the amount and temperature of cooling water and the metal composition.
In the past, two methods have been employed for determining mold velocity. In one method, a rod rests on the top of the mold table. As the rod passes a given point, the operator of the casting station places a mark on the rod, at specific time intervals. By noting the distance between markings passing this point, the operator determines the average mold velocity, making adjustments as he believes necessary. This, of course, is a crude calculation, depending on eyeball sightings of movements as small as 1.0 inch (2.54 centimeters)/minute, and does not lend itself to an automated operation whereby continual calculations and modifications of table velocity to produce high quality ingots could be accomplished.
The other method commonly employed for measuring mold velocity is based on the fact that the table carrying the mold is hydraulically operated. Thus, as the table moves downwardly, hydraulic fluid is displaced. The operator can measure, through flow meter and other techniques, the rate of fluid displacement and correlate this to table velocity. However, such a system cannot account for leaks in the hydraulic system and is thus inaccurate.
It is thus desirable to provide a method and apparatus for determining mold velocity which measures mold velocity directly, i.e., without indirect measurement of secondary occurrences to calculate mold velocity, and which permits continuous measurement of this velocity for an automated optimization of mold velocity.